In a number of prior applications and patents mentioned in the above-identified copending application and in the latter, there are described vessels or containers which have been found to be useful in the transport and storage of radioactive material and especially irradiated nuclear fuel elements.
These containers have in common the fact that they comprise a vessel which can be cast from a cast iron, especially spherulitic or nodular cast iron or cast steel, which is open at its upper end and has comparatively thick walls and a bottom, and into which the irradiated fuel elements can be introduced. The mouth of the vessel is sealed by a plug-like cover which has a projecting portion fitting into the mouth and a flange supporting the projecting portion and a shoulder surrounding the mouth.
As described in the aforementioned application, various types of seals may be provided between this cover and the vessel and the plug-type cover, also of cast iron or cast steel, and the thick walls and bottom of the container are all dimensioned so that practically no radiation from the interior reaches the environment.
In the numerous applications and patents referred to in the specifically identified parent application hereof, it has been pointed out that it may be advantageous to provide the outer wall of the vessel with ribs or vanes to promote dissipation of heat to ambient fluids, and that the wall of the vessel can be provided with passages in such orientation and number as to enable them to contain materials with a high neutron-capture cross section or other affinity for the capture of radiation so that practically a complete curtain for such radiation capture is provided within the wall surrounding the nuclear fuel elements.
The wall may also be provided with a passage opening into the space defined within the container and in which the radioactive fuel elements can be disposed for introducing fluids or for sampling. Security can be ensured by providing one or more additional covers above the shielding or plug-type cover which themselves can be sealed to the vessel and which can define monitoring spaces with each next inwardly disposed cover. By monitoring fluids entering these spaces, the failure of a container seal can be ascertained.
These and other arrangements described in the aforementioned applications have contributed to the success of such containers in the handling of radioactive materials.
In application Ser. No. 243,627 U.S. Pat. No. 4,528,454, however, a special organization of the covers has been described in which the shielding cover is seated in a stepped seat of the mouth of the container and O-rings or like sealing members are provided between juxtaposed surfaces of this seat and the plug-type cover. An additional cover was applied to the container and likewise was sealed with respect to the latter by such sealing means.
The shielding cover was formed with a central projection and integral therewith but thereabove, an outwardly extending circumferential flange of cylindrical configuration, this flange being received in a cylindrical portion of the step defining an inwardly extending shoulder at the step upon which the flange rests and to which the flange can be connected by flange bolts traversing the flange and threadedly engaging in bores which open at the shoulder of the stepped mouth of the container.
To this end, bolt bores are provided in the flange for registry with the threaded bores in the container wall. In addition, the plug-type cover can have a multiplicity of cover bores which can communicate with the space defined by the container directly or with bores in the wall of the container which, in turn, communicate with the storage space of the container, these bores serving as control bores or for monitoring, filling or sampling purposes. The control bores open into an annular control compartment between spaced-apart seals. Frequently, complex means must be used to seal these additional bores and, in general, the control and monitor bores provided in the plug-type cover.
While the system described in this latter application has proved to be highly effective for the purposes described, it has now been found to be possible to improve upon it.